1. Field of the Invention
This invention relates to an arrangement (apparatus and method) for simulating radar targets. More particularly, this arrangement delays radar transmissions to generate simulated reflections from a single simulated target.
2. Description of the Prior Art
There are two commonly used techniques for generating delayed transmit pulses, each of which has certain operational disadvantages or difficulties.
The most commonly used technique utilizes a series of counters Each counter is programmed to output a pulse a given number of clock cycles after a transmit signal is introduced to the counter. Successive transmit pulses are supplied to successive counters The outputs of the counters are then multiplexed to form a composite delayed reflection signal.
One problem with this technique is that the pulse width of the delayed pulses is not the same as the pulse widths of the input pulses In the prior art multiple counter scheme, the duration of the pulses output from the counters are a fixed number of clock cycles Therefore, more circuitry must be added to modify pulse widths in the composite signal to duplicate pulse widths in the input signal.
Another problem with this technique is that a large number of counters is required when the desired delay is greater than the time between transmit pulses. Because each counter must output its delayed transmit pulse before it can accept another input pulse, delay processors utilizing this technique may require excessive numbers of parallel counters.
The second technique commonly used in delay processors utilizes a pulse generator to delay incoming transmit pulses. A certain amount of time after an input pulse triggers the pulse generator, a pulse of a predetermined fixed duration is generated. Therefore, as in the multiple counter method, the output pulses do not maintain the pulse width of the input pulses. The pulse width of the output pulse is preprogrammed and static. Furthermore, pulse generators ignore their inputs when delaying previous pulses. The pulse generator technique, therefore, suffers the additional disadvantage that in a rapid succession of pulses not all transmit pulses generate corresponding output pulses.
Both of these known techniques of simulating target reflections, the multiple counter scheme and the pulse generator scheme, present problems when the desired delay of the delay processor is greater than the period between transmit pulses. The counter technique requires excessive hardware and the pulse generator technique fails to generate output pulses. In addition, neither of these schemes outputs an output pulse stream whose pulse widths corresponds to the pulse widths in the input pulse stream.